Create a draft form A/B setup from an existing popup, flyout or fullscreen form. Only those display types are eligible;
the source form becomes the setup's main form and its two variants start as identical copies that can be edited
independently afterward. The setup is created in draft status and does not serve traffic until started via
POST /form-ab-setups/{abSetupID}/start.

Each variant carries a traffic-distribution weight. When versions is omitted, both variants receive a weight
of 50; otherwise each weight must be at least 1 and the weights must sum to 100.

Scopes:
forms.write

Rate Limiting:
This endpoint is rate limited to 400 requests per minute.